Piezoelectric unit, liquid ejecting head, and liquid ejecting apparatus

ABSTRACT

In an inactive region, a farthest dummy electrode formed in a base end portion and an isolated dummy electrode island are located at positions along an extension from an individual internal electrode toward the base end portion. Such a configuration allows the area of the dummy electrode to be reduced, compared with a dummy electrode continuously formed in the inactive region. Therefore, the cost incurred by the dummy electrode is reduced, which leads to reduction in manufacturing cost of a piezoelectric unit.

This application claims a priority to Japanese Patent Application No.2011-186965 filed on Aug. 30, 2011 which is hereby expresslyincorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a piezoelectric unit to be displacedupon applying a voltage to a piezoelectric element, and a liquidejecting head and a liquid ejecting apparatus that include thepiezoelectric unit.

2. Related Art

A liquid ejecting head has thus far been known that includes a vibrationplate constituting a part of a pressure chamber communicating with anozzle opening through which ink droplets, an example of the liquid, aredispensed, in which the vibration plate is deformed by a piezoelectricelement so as to pressurize the ink in the pressure chamber to therebydispense the ink droplets through the nozzle opening. As well, a liquidejecting apparatus including such a liquid ejecting head is also known.Some ink jet recording heads, exemplifying the liquid ejecting head,employ a vertical vibration type piezoelectric unit that expands andcontracts in an axial direction of the piezoelectric element. Thevertical vibration type piezoelectric unit thus far developed includethe one having a piezoelectric element block that includes a pluralityof multilayer piezoelectric elements each including a common internalelectrode, an individual internal electrode, and a piezoelectricmaterial layer interposed therebetween, the piezoelectric element blockbeing connected to a fixing substrate, for example as disclosed inJP-A-2004-327462.

The piezoelectric element block includes a distal end portion which is afree end, and a base end portion connected to the fixing substrate, anda driver wiring is connected to the base end portion. The commonexternal electrode connected to the common internal electrode and theindividual external electrode connected to the individual internalelectrode are formed so as to reach the base end portion, and the driverwiring is connected to the common external electrode and the individualexternal electrode at the base end portion.

Normally, a silver/palladium alloy is employed as the material of thecommon internal electrode and the individual internal electrode, becauseof the sintering shrinkage that agrees with that of the piezoelectricmaterial layer, close adhesion therewith, and high reliability (see, forexample, JP-A-2011-56731 and JP-A-2011-71365).

However, the palladium, which is a rare metal, contained in thesilver/palladium alloy constituting the common internal electrode andthe individual internal electrode inevitably raises the manufacturingcost. Although a part of the common internal electrode or individualinternal electrode located in an inactive region which is not involvedin the vibration performance may be excluded for the purpose of costreduction, in which case, however, the thickness of the base end portionin the inactive region where those electrodes are layered is changed,and therefore the connection with the driver wiring and positioningtherewith by connection to the fixing substrate become difficult.

Therefore, it has been difficult to reduce the manufacturing cost of thepiezoelectric unit, the liquid ejecting head, and the liquid ejectingapparatus while keeping the thickness of the base end portion of thepiezoelectric element block unchanged.

SUMMARY

Accordingly, the invention may be advantageously realized as thefollowing application examples and embodiments.

Application Example 1

A first application example represents a piezoelectric unit thatincludes a plurality of piezoelectric elements formed along a pluralityof slits so as to extend from a first end portion of a piezoelectricelement block toward a second end portion thereof, and a circuit boardwith a driving electrode formed on a surface thereof. The piezoelectricelements each include an active region in which a first internalelectrode, a second internal electrode, a piezoelectric material layerinterposed between the first internal electrode and the second internalelectrode, and an insulative outer layer are stacked. The piezoelectricelement block includes an inactive region in which the first internalelectrode extending from the active region as far as the second endportion, a first dummy electrode formed on the second end portion at aposition along an extension from the second internal electrode towardthe second end portion, at least one isolated second dummy electrodeformed between the second internal electrode and the first dummyelectrode, the piezoelectric material layer and the outer layer arestacked, a first external electrode connected to the first internalelectrode at an end face of the second end portion, and a secondexternal electrode connected at an end face of the first end portion tothe second internal electrode extending through the active region so asto reach the first end portion. The first external electrode and thesecond external electrode are formed so as to extend as far as a surfaceof the outer layer on one side of the inactive region, and the drivingelectrode is connected to the first external electrode and the secondexternal electrode located in the inactive region.

In this application example, the first dummy electrode and the isolatedsecond dummy electrode are located on the second end portion of thepiezoelectric element block at the position along the extension from thesecond internal electrode toward the second end portion, in the inactiveregion. Such a configuration allows the area of the dummy electrode tobe reduced, compared with the dummy electrode continuously formed in theinactive region. Therefore, the cost incurred by the dummy electrode isreduced, which leads to reduction in manufacturing cost of thepiezoelectric unit.

In addition, at least one isolated second dummy electrode is provided inthe inactive region between the second internal electrode and the firstdummy electrode. In this case, the portion of the inactive region wherethe first dummy electrode and the second dummy electrode are providedcan maintain the same thickness as that of the active region unlike inthe case where the isolated second dummy electrode is not provided, andhence fluctuation in thickness of the piezoelectric element block in theinactive region can be suppressed. Such a configuration allows the firstexternal electrode and the second external electrode, extending to thesurface of the outer layer on the one side of the inactive region, toremain generally flat. In the piezoelectric unit thus configured,therefore, the driving electrode formed on the one surface of thecircuit board can be connected along a flat surface to the firstexternal electrode and the second external electrode.

Application Example 2

In the foregoing piezoelectric unit, the first internal electrode andthe second internal electrode may contain a silver/palladium alloy.

In this case, consumption of palladium which is a rare metal can bereduced, which leads to further reduction in manufacturing cost of thepiezoelectric unit.

Application Example 3

In the foregoing piezoelectric unit, the driving electrode may beconnected to the first external electrode and the second externalelectrode through an anisotropic conductive layer. In this case, sincethe first external electrode and the second external electrode aregenerally flatly formed, the anisotropic conductive layer uniformlycollapses when a pressure is imposed thereon for achieving theconnection. Accordingly, contacts among the metal particles in theanisotropic conductive layer can be secured, and therefore theconnection between the driving electrode formed on the one surface ofthe circuit board and the first external electrode and the secondexternal electrode can be assured.

Application Example 4

In the foregoing piezoelectric unit, the first internal electrode mayserve as a common internal electrode of the plurality of piezoelectricelements, and the second internal electrode may serve as an individualinternal electrode of each of the plurality of piezoelectric elements.

In this application example, the first internal electrode extends fromthe active region to the second end portion of the piezoelectric elementblock, and is connected to the first external electrode at the end faceof the second end portion. Such a configuration facilitates theformation of the common electrode. On the other hand, the secondinternal electrode extends through the active region to the first endportion of the piezoelectric element block, and is connected to thesecond external electrode at the end face of a distal end portion of thepiezoelectric element formed along the slits extending from the firstend portion toward the second end portion of the piezoelectric elementblock. Such a configuration facilitates the formation of the individualelectrode.

Application Example 5

A fifth application example represents a liquid ejecting head thatincludes a nozzle plate perforated with nozzle openings through which aliquid is ejected, a flow path plate coupled with the nozzle plate andincluding a part of a pressure chamber communicating with the nozzleopening, and a vibration plate constituting a part of the pressurechamber. The inactive region of the piezoelectric unit is fixed to aflat fixing substrate at a predetermined position, and the first endportion is disposed in contact with the vibration plate.

In addition to the foregoing advantageous effects, since the thicknessof the inactive region of the piezoelectric element block is maintainedgenerally uniform and the surface thereof is generally flat, theinactive region can be coupled with the flat fixing substrate with highpositioning accuracy and therefore the first end portion of thepiezoelectric element is barely shifted from the desired contactposition on the vibration plate. Consequently, the extension andcontraction of the piezoelectric element can be efficiently transmittedto the vibration plate, which enables the liquid ejecting head toaccurately eject a predetermined amount of liquid.

Application Example 6

A sixth application example represents a liquid ejecting apparatus thatincludes the foregoing liquid ejecting head.

With such a configuration, the liquid ejecting apparatus equallyprovides the foregoing advantageous effects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view showing an ink jet recordingapparatus.

FIG. 2A is a schematic cross-sectional view of an ink jet recordinghead, and FIG. 2B is a fragmentary plan view thereof.

FIG. 3 is a schematic perspective view of a piezoelectric unit viewedfrom the side of a piezoelectric element.

FIG. 4A is a schematic plan view of the piezoelectric unit according tothe embodiment, and FIG. 4B is a schematic cross-sectional view takenalong a line IVB-IVB in FIG. 4A.

FIG. 5 is a cross-sectional view of the piezoelectric unit according toan inventive example, corresponding to the cross-sectional view takenalong the line IVB-IVB in FIG. 4A.

FIG. 6 is a graph showing a relationship between a distance in which adummy electrode is not located and a depth of a recess and an overallthickness at the position where the dummy electrode is not located.

FIG. 7 is a cross-sectional view of a piezoelectric unit according tocomparative examples 1 and 2, corresponding to the cross-sectional viewtaken along the line IVB-IVB in FIG. 4A.

FIG. 8 is a cross-sectional view of a piezoelectric unit according to aconventional example, corresponding to the cross-sectional view takenalong the line IVB-IVB in FIG. 4A.

FIG. 9 is a cross-sectional view of a piezoelectric unit according to avariation, corresponding to the cross-sectional view taken along theline IVB-IVB in FIG. 4A.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereafter, an embodiment of will be described in details referring tothe drawings. In the drawings hereafter referred to, layers andcomponents may be illustrated in scales different from the actual ones,for the sake of better visual understanding.

FIG. 1 is a schematic perspective view showing an ink jet recordingapparatus 100 according to the embodiment, exemplifying the liquidejecting apparatus.

As shown in FIG. 1, the ink jet recording apparatus 100 includes acarriage 101. The carriage 101 is made to reciprocate in an axialdirection of a platen 105 along a guide member 104, by a timing belt 103driven by a carriage motor 102.

For example an ink jet recording head 300, an example of the liquidejecting head to be subsequently described, is mounted on the carriage101 at a position to oppose recording paper 200.

In addition, on the ink jet recording head 300, a black ink cartridge106 and a color ink cartridge 107 that supply ink, which is an exampleof the liquid, to the ink jet recording head 300 are removably mounted.

The recording paper 200 is disposed in a printing region P, so that theink jet recording head 300 dispenses the ink on the recording paper 200for printing characters or images.

Further, as shown in FIG. 1, in a home position H which is anon-printing region where the recording paper 200 is not located, forexample a cap 120, a suction pump 130, and a wiper 140 are located so asto constitute a cleaning unit.

FIGS. 2A and 2B schematically depict the ink jet recording head 300.FIG. 2A is a schematic cross-sectional view thereof, and FIG. 2B is afragmentary plan view thereof.

Referring to FIGS. 2A and 2B, the ink jet recording head 300 includes apiezoelectric unit 10, a flow path plate 60, a vibration plate 65, anozzle plate 67 perforated with nozzle openings 66, and a head case 68.

The piezoelectric unit 10 includes a plurality of piezoelectric elements11, a piezoelectric element block 13, a common external electrode 21exemplifying the first external electrode, an individual externalelectrode 22 exemplifying the second external electrode, and a circuitboard 50.

The circuit board 50 may be constituted, for example, of a chip on film(COF) including a driver IC 52 mounted on a driver wiring 51.

The circuit board 50 is connected to the individual external electrode22 and the common external electrode 21, for example through electrodepads 26. The circuit board 50 also includes an insulation layer 53,except for the region where the driver wiring 51 is connected to theelectrode pads 26.

The flow path plate 60 is formed of a silicon monocrystalline substrate,and pressure chambers 62 each defined by partition walls 61 are alignedin a width direction of the flow path plate 60, along one of the sidesthereof. On an end portion of each pressure chamber 62 in a longitudinaldirection thereof, a reservoir 63 for supplying the ink to the pressurechamber 62 is provided so as to communicating therewith through an inkoutlet 64. The face of the flow path plate 60 on the side of the openingof the pressure chamber 62 is covered with the vibration plate 65, andthe nozzle plate 67 perforated with the nozzle openings 66 is bonded tothe opposite face of the flow path plate 60 with an adhesive, a hot-meltfilm, or the like.

The head case 68 having ink supply paths communicating with the blackink cartridge 106 and the color ink cartridge 107 shown in FIG. 1 isfixed to the vibration plate 65, and the piezoelectric unit 10 is fixedto the head case 68 at a position determined with high accuracy by meansof fixing substrate 14 having a flat plate shape. More specifically, thepiezoelectric unit 10 is positioned such that the tip portion, i.e. thedistal end portion of each piezoelectric element 11 contacts one ofpedestals 69 formed on the vibration plate 65 at positions correspondingto the respective pressure chambers 62. The fixing substrate 14 may beformed, for example, by punching a stainless steel plate.

The piezoelectric unit 10 will now be described in details hereunder.

FIG. 3 is a schematic perspective view of the piezoelectric unit 10viewed from the side of the piezoelectric element 11. FIG. 4A is aschematic plan view thereof, and FIG. 4B is a schematic cross-sectionalview taken along a line IVB-IVB in FIG. 4A. In these drawings, thecircuit board 50 is not illustrated.

As shown in FIGS. 3, 4A and 4B, the piezoelectric unit 10 includes apiezoelectric element block 13 including a row 12 formed of theplurality of piezoelectric elements 11 aligned in the width directionthereof. The distal end portion 131 of the piezoelectric element block13 constitutes a free end, and the fixing substrate 14 is connected tothe opposite end portion, i.e. a base end portion 132.

Referring to FIGS. 2A and 4B, a part of the piezoelectric element block13 is composed of a piezoelectric material layer 15, and internalelectrodes constituting two poles of the piezoelectric element 11,namely an individual internal electrode 16, exemplifying the secondinternal electrode and constituting an individual electrode electricallyindependent from the adjacent piezoelectric element 11, and a commoninternal electrode 17, exemplifying the first internal electrode andconstituting a common electrode electrically common with the adjacentpiezoelectric element 11, the individual internal electrode 16 and thecommon internal electrode 17 being alternately stacked in thepiezoelectric material layer 15.

It is preferable to employ a silver/palladium alloy to form theindividual internal electrode 16 and the common internal electrode 17,because of the sintering shrinkage that agrees with that of thepiezoelectric material layer 15, close adhesion therewith, and highreliability.

In addition, an upper outer layer 15 a and a lower outer layer 15 b,formed of an insulative piezoelectric material, are stacked so as toform outer layers.

The piezoelectric element block 13 may be formed, for example, bystacking a green sheet formed of a slurry containing a dielectric toconstitute the piezoelectric material layer 15, the upper outer layer 15a, and the lower outer layer 15 b, powder of a conductive material toform the individual internal electrode 16 and the common internalelectrode 17, and a paste containing non-volatile organic components,and sintering the stacked structure. By the sintering, the volume of thegreen sheet and the paste is reduced.

Here, the number of layers shown in FIGS. 2A and 4B is only exemplary,and a different structure may be adopted.

A plurality of slits 18 are formed in the piezoelectric element block 13with a wire saw for example, such that a portion thereof on the side ofthe distal end portion 131 is split in a comb teeth shape, and thus therow 12 of the piezoelectric elements 11 is formed.

When a voltage is applied between the individual internal electrode 16and the common internal electrode 17 constituting the piezoelectricelement 11, primarily an active region A, corresponding to the side ofthe distal end portion 131 not connected to the fixing substrate 14, iscaused to vibrate. On the respective outer sides of the row 12 of thepiezoelectric elements 11, positioning members 19 wider than theindividual piezoelectric elements 11 are provided. The positioningmembers 19 serve for accurate positioning of the piezoelectric unit 10with respect to the ink jet recording head 300 shown in FIG. 2, when thepiezoelectric unit 10 is mounted thereon.

In each of the piezoelectric elements 11, the individual internalelectrode 16 is formed so as to extend from the distal end portion 131through the active region A, i.e., to the vicinity of a positioncorresponding to an end face 14 a of the fixing substrate 14. Inaddition, a farthest dummy electrode 16 b exemplifying the first dummyelectrode, and a dummy electrode island 16 a exemplifying the isolatedsecond dummy electrode are provided along the extension from theindividual internal electrode 16 toward the base end portion 132. Thefarthest dummy electrode 16 b is located at the base end portion 132,and the dummy electrode island 16 a is located between the individualinternal electrode 16 and the farthest dummy electrode 16 b.

On the other hand, the common internal electrode 17 serving as thecommon electrode is formed so as to extend through the active region Aas far as the base end portion 132. The portion of the piezoelectricelement 11 attached to the fixing substrate 14, where the individualinternal electrode 16 is not located, constitutes an inactive region Ithat is barely involved in the vibration.

The common external electrode 21, connected to the common internalelectrode 17, is provided on a surface of one side of the piezoelectricelement block 13 (in this embodiment, surface 134 opposite a surface 133attached to the fixing substrate 14), as well as on an end face 13 a ofthe base end portion 132. The connection between the common internalelectrode 17 and the common external electrode 21 is made at the endface 13 a of the base end portion 132.

On the surface 134 and an end face 13 b of the distal end portion 131,the individual external electrode 22 is provided which is split so as tocorrespond to each piezoelectric element 11 such that each split segmentbecomes electrically independent, and connected to the individualinternal electrode 16.

The common external electrode 21 and the individual external electrode22 are formed so as to reach the surface 134 of the inactive region I,and the driver wiring 51 is connected to the common external electrode21 and the individual external electrode 22 located in the inactiveregion I.

The common external electrode 21 and the individual external electrode22 will be described in further details here below. The common externalelectrode 21 is continuously provided over a region including therespective corner portions 135 on the side of the base end portion 132of the surface 134 of the piezoelectric element block 13 and the endface 13 a of the base end portion 132.

On the other hand, the individual external electrode 22 is continuouslyprovided over a region including the end face 13 b of the distal endportion 131 and the surface 134 of the piezoelectric element block 13.On the surface 134, the individual external electrode 22 extends in thedirection in which the slits 18 are formed, so as to overlap a part of aregion between the portions of the common external electrode 21 locatedin the vicinity of the respective corner portions 135 on the surface 134of the piezoelectric element block 13.

In addition, a region on the surface 134 between the base end portion132 and the individual external electrode 22 is constituted as a regionwithout electrode 24 where the individual external electrode 22 is notlocated.

Referring again to FIGS. 1, 2A and 2B, in the ink jet recording head 300thus configured, the ink is supplied to the reservoir 63 through the inksupply path communicating with the black ink cartridge 106 and the colorink cartridge 107, and distributed to the respective pressure chambers62 through the ink outlet 64.

More specifically, upon applying a voltage to the piezoelectric unit 10the piezoelectric unit 10 is made to contract. Accordingly the vibrationplate 65 is lifted together with the piezoelectric unit 10, and thevolume of the pressure chamber 62 is expanded so that the ink isintroduced into the pressure chamber 62. After the pressure chambers 62are filled with the ink so as to reach the nozzle opening 66, when thepiezoelectric unit 10 is released from the voltage thus far appliedthereto in accordance with a recording signal from the driver circuit,the piezoelectric unit 10 is prolonged so as to resume the initialstate. Therefore, the vibration plate 65 is also displaced so as toresume the initial state and the pressure chamber 62 is made tocontract, so that the ink droplet is dispensed through the nozzleopening 66 because of the increase in internal pressure.

The foregoing embodiment offers the following advantageous effects.

(1) In the inactive region I, the farthest dummy electrode 16 b formedin the base end portion 132 and the isolated dummy electrode island 16 aare located at the positions extended from the individual internalelectrode 16 toward the base end portion 132. Such a configurationallows the area of the dummy electrode to be reduced, compared with thedummy electrode continuously formed in the inactive region I. Therefore,the cost incurred by the dummy electrode is reduced, which leads toreduction in manufacturing cost of the piezoelectric unit 10.

In addition, at least one isolated dummy electrode island 16 a isprovided in the inactive region I between the individual internalelectrode 16 and the farthest dummy electrode 16 b. Accordingly, theportion of the inactive region I where the dummy electrode island 16 aand the farthest dummy electrode 16 b are provided can maintain the samethickness as that of the active region A, unlike in the case where theisolated dummy electrode island 16 a is not provided, and hencefluctuation in thickness of the piezoelectric element block 13 in theinactive region I can be suppressed. Such a configuration allows theindividual external electrode 22 and the common external electrode 21,extending to the surface 134 of the inactive region I, to remaingenerally flat. In the piezoelectric unit 10, therefore, the driverwiring 51 provided on the one side of the circuit board 50 can beconnected along a flat surface to the common external electrode 21 andthe individual external electrode 22.

(2) Consumption of palladium which is a rare metal can be reduced, whichleads to further reduction in manufacturing cost of the piezoelectricunit 10.

(3) Since the individual external electrode 22 and the common externalelectrode 21 are generally flatly formed, the electrode pad 26 uniformlycollapses when a pressure is imposed thereon for achieving theconnection. Accordingly, contacts among the metal particles in theelectrode pad 26 can be secured, which allows the piezoelectric unit 10to provide assured connection between the driver wiring 51 formed on theone surface of the circuit board 50, and the individual externalelectrode 22 and the common external electrode 21.

(4) The common internal electrode 17 extends from the active region A tothe base end portion 132 of the piezoelectric element block 13 and isconnected to the common external electrode 21 at the end face 13 a ofthe base end portion 132. With such a configuration, the piezoelectricunit 10 facilitates the formation of the common electrode. On the otherhand, the individual internal electrode 16 extends through the activeregion A to the distal end portion 131 of the piezoelectric elementblock 13, and is connected to the individual external electrode 22 atthe end face 13 b of the distal end portion 131 of the piezoelectricelements 11 formed along the slits 18 extending from the distal endportion 131 toward the base end portion 132 of the piezoelectric elementblock 13. With such a configuration, the piezoelectric unit 10facilitates the formation of the individual electrode.

(5) In addition to the foregoing advantageous effects, since thethickness of the inactive region I of the piezoelectric element block 13is maintained generally uniform and the surface thereof is generallyflat, the inactive region I can be coupled with the flat fixingsubstrate 14 with high positioning accuracy and therefore the distal endportion 131 of the piezoelectric element 11 is barely shifted from thedesired contact position on the vibration plate 65. Consequently, theextension and contraction of the piezoelectric element 11 can beefficiently transmitted to the vibration plate 65, which enables theliquid ejecting head 300 to accurately eject a predetermined amount ofliquid.

(6) The liquid ejecting apparatus 100 equally provides the foregoingadvantageous effects.

The foregoing embodiment will be described more specifically, referringto an inventive example, comparative examples 1 and 2, and aconventional example.

Inventive Example

FIG. 5 illustrates further details of the cross-sectional view takenalong the line IVB-IVB in FIG. 4A. The piezoelectric material layer 15is composed of 13 layers including the upper outer layer 15 a and thelower outer layer 15 b, in other words the piezoelectric material layer15 interposed between the individual internal electrode 16 and thecommon internal electrode 17 is composed of 11 layers.

Now, the thickness of the piezoelectric element block 13 will be denotedas a, the length of the active region A will be denoted as b, thedistance between the individual internal electrode 16 and the dummyelectrode island 16 a will be denoted as c, the length of the dummyelectrode island 16 a will be denoted as d, the distance between thedummy electrode island 16 a and the farthest dummy electrode 16 b willbe denoted as e, the length of the farthest dummy electrode 16 b will bedenoted as f, and the distance in the longitudinal direction between theend face 14 a of the fixing substrate 14 and the dummy electrode island16 a will be denoted as g. All above indicate the distance or lengthalong the direction from the base end portion 132 toward the distal endportion 131, except for the thickness.

In the inventive example, the foregoing dimensions were set as a=0.28mm, b=1.20 mm, c=0.62 mm, d=0.20 mm, e=0.35 mm, f=0.13 mm, and g=0.55mm. Here, d may be 0.10 mm and e may be 0.45 mm.

FIG. 6 is a graph in which the horizontal axis represents the distance cbetween the individual internal electrode 16 and the dummy electrodeisland 16 a or the distance e between the dummy electrode island 16 aand the farthest dummy electrode 16 b (distance through which the dummyelectrode is not present), and the vertical axis represents the depth ofrecesses 130 a, 130 b, and 130 c and the overall thickness of theportion where the dummy electrode is not present, with respect to theinventive example, the comparative examples 1 and 2, and theconventional example.

As stated above, the inventive example corresponds to 0.62 mm, 0.45 mm,and 0.35 mm of the horizontal axis.

The recesses 130 a, 130 b, and 130 c are formed because the extent ofcontraction differs by positions depending on whether the paste forforming the dummy electrode is provided.

When the distance without the dummy electrode increases, the recessbecomes deeper and hence the overall thickness decreases. The depth ofthe recess and the overall thickness are generally linearly proportionalto the distance without the dummy electrode.

In the inventive example, the depths of the recess corresponding toc=0.62 mm, e=0.45 mm, and e=0.35 mm were 0.5 μm, 0.2 μm, and 0.0 μm,respectively.

With the depth of 0.5 μm or less, no problem arose in the connectionbetween the circuit board 50 and the common external electrode 21 andthe individual external electrode 22.

In addition, the inventive example had two portions where the overallthickness a was secured (corresponding to the dummy electrode island 16a and the farthest dummy electrode 16 b), which could be placed on aregion outside of a sag portion 14 b on the flat fixing substrate 14,when the piezoelectric element block 13 was fixed. Therefore, therelative position between the inactive region I and the flat fixingsubstrate 14 was barely shifted.

The sag portion 14 b is prone to be formed on an end portion of thefixing substrate 14, in the case where the fixing substrate 14 is formedby punching a stainless steel plate. It is preferable to locate thedummy electrode island 16 a at a position deviated from the sag portion14 b. For example, in the case where the sag portion 14 b is formed in amaximum width of 0.5 mm from the edge, it is preferable to set thedistance g between the end face 14 a of the fixing substrate 14 and thedummy electrode island 16 a as approximately 0.55 mm.

Comparative Example 1

FIG. 7 is a cross-sectional view of the comparative example 1.

The comparative example 1 is different from the inventive example in notincluding the dummy electrode island 16 a. The distance h between theindividual internal electrode 16 and the farthest dummy electrode 16 bwas set as 1.10 mm. The structure and dimensions of the remainingportions were the same as those of the embodiment.

The depth of the recess was 2.7 μm corresponding to h=1.10 mm in FIG. 6,and a sloped portion 130 d was formed along the periphery of the recess130 c. Because of the sloped portion 130 d, the portion of theindividual external electrode 22 in the inactive region I could not bekept flat and therefore the contact between the circuit board 50 and theindividual external electrode 22 was imperfect.

In addition, the comparative example 1 had only one position where theoverall thickness a was secured (corresponding to the position where thefarthest dummy electrode 16 b is located) in a region outside of the sagportion 14 b of the flat fixing substrate 14, and therefore thepiezoelectric element block 13 was fixed with an inclination, and thepositioning between the inactive region I and the flat fixing substrate14 was remarkably shifted.

Comparative Example 2

The comparative example 2 is different from the comparative example 1only in that the distance h between the individual internal electrode 16and the farthest dummy electrode 16 b is 2.09 mm.

The depth of the recess was 4.6 μm corresponding to h=2.09 mm in FIG. 6,and a large sloped portion 130 d was formed along the periphery of therecess 130 c. Because of the sloped portion 130 d, the portion of theindividual external electrode 22 in the inactive region I could not bekept flat and therefore the contact between the circuit board 50 and theindividual external electrode 22 was imperfect, as with the comparativeexample 1.

Conventional Example

FIG. 8 is a cross-sectional view of the conventional example,corresponding to the cross-sectional view taken along the line IVB-IVBin FIG. 4A. In the conventional example, neither the dummy electrodeisland 16 a nor the farthest dummy electrode 16 b was formed unlike inthe inventive example, and a dummy electrode 16 c is formed from thebase end portion 132 to the vicinity of the individual internalelectrode 16. The dummy electrode 16 c is spaced from the individualinternal electrode 16 by a distance i, which is 0.15 mm for example. Therecess is barely formed in the conventional example.

[Variation]

FIG. 9 is a cross-sectional view of a variation, corresponding to thecross-sectional view taken along the line IVB-IVB in FIG. 4A. In thevariation, the dummy electrode islands 16 d are provided at fourpositions. Although it is preferable to shorten the length j of thedummy electrode island 16 d from the viewpoint of the cost, the limit ofthe length depends, for example, on a minimum printable length. In thecase where the minimum printable length is 0.1 mm, the lower limit ofthe length of the dummy electrode island 16 d is 0.1 mm. To determinethe distance k between the dummy electrode islands 16 d, a pointcorresponding to the depth of recess of 0.5 μm or less may be selectedin the graph of FIG. 6, in other words a distance without dummyelectrode of 0.62 mm or less may be selected.

Here, the number of dummy electrode islands 16 d is not limited to four,but may be any desired number.

Various modifications may be made to the foregoing embodiment.

For example, the configuration of the common external electrode 21 andthe individual external electrode 22 provided on the surface 134 of thepiezoelectric element block 13 is not limited to the foregoingembodiment.

Although the slits 18 are formed so as not to reach the end face 13 a ofthe piezoelectric element block 13 in the embodiment, the slits 18 maybe formed so as to reach the end face 13 a of the piezoelectric elementblock 13. On the end face 13 a of the piezoelectric element block 13,the common external electrode 21 is provided except in the region closeto the end portion on the respective sides. Accordingly, even though apart of the common internal electrode 17 stacked in the piezoelectricelement 11 is completely split into segments in each of thepiezoelectric element 11 because of forming the slits 18 so as to reachthe end face 13 a of the piezoelectric element block 13, electricalconnection between each of the split segments of the common internalelectrode 17 can be secured by the common external electrode 21 providedon the end face 13 a.

In the embodiment, the individual external electrode 22 is formed over aregion slightly larger than the region corresponding to the row 12 ofthe piezoelectric elements 11, so that the individual external electrode22 is also provided on a part of the positioning member 19. By thusforming the individual external electrode 22 integrally over a distancelonger than the length of the row 12 of the piezoelectric elements 11,the individual external electrode 22 can be surely provided on each ofthe piezoelectric elements 11 when split by the slits 18, even thoughthe slits 18 are formed at slightly deviated positions.

Further, although the region without electrode 24 is provided throughoutthe region on the surface 134 of the piezoelectric element block 13between the base end portion 132 and the individual external electrode22 in the embodiment, an electrode layer may be provided along the baseend portion 132, so that the common external electrode 21 iscontinuously provided so as to cover the surface 134 of thepiezoelectric element block 13.

Further, although the common external electrode 21 is connected to thecommon internal electrode 17 at the end face 13 a of the base endportion 132 of the piezoelectric element block 13 in the embodiment,different configurations may be adopted. For example, the commonexternal electrode 21 may be formed on the respective side faces of thepiezoelectric element block 13 in the width direction, namely side faces13 c, 13 d thereof, so as to be connected to the common internalelectrode 17 at the side faces 13 c, 13 d of the piezoelectric elementblock 13. Alternatively, the common external electrode 21 may becontinuously formed over a region including the side faces 13 c, 13 d ofthe piezoelectric element block 13 and the end face 13 a thereof.

What is claimed is:
 1. A piezoelectric unit, comprising: a plurality ofpiezoelectric elements formed along a plurality of slits so as to extendfrom a first end portion of a piezoelectric element block toward asecond end portion thereof; and a circuit board with a driving electrodeformed on a surface thereof, wherein the piezoelectric elements eachinclude an active region in which a first internal electrode, a secondinternal electrode, a piezoelectric material layer interposed betweenthe first internal electrode and the second internal electrode, and aninsulative outer layer are stacked, the piezoelectric element blockincludes an inactive region in which the first internal electrodeextending from the active region as far as the second end portion, afirst dummy electrode formed on the second end portion at a positionalong an extension from the second internal electrode toward the secondend portion, at least one isolated second dummy electrode formed betweenthe second internal electrode and the first dummy electrode, thepiezoelectric material layer, and the outer layer are stacked; a firstexternal electrode connected to the first internal electrode at an endface of the second end portion; and a second external electrodeconnected to the second internal electrode at an end face of the firstend portion, the second internal electrode extending through the activeregion so as to reach the first end portion, and the first externalelectrode and the second external electrode are formed so as to reach asurface of the outer layer on one side of the inactive region, and thedriving electrode is connected to the first external electrode and thesecond external electrode located in the inactive region.
 2. Thepiezoelectric unit according to claim 1, wherein the first internalelectrode and the second internal electrode contain a silver/palladiumalloy.
 3. The piezoelectric unit according to claim 1, wherein thedriving electrode is connected to the first external electrode and thesecond external electrode through an anisotropic conductive layer. 4.The piezoelectric unit according to claim 1, wherein the first internalelectrode serves as a common internal electrode of the plurality ofpiezoelectric elements, and the second internal electrode serves as anindividual internal electrode of each of the plurality of piezoelectricelements.
 5. A liquid ejecting head, comprising: a nozzle plateperforated with nozzle openings through which a liquid is ejected; aflow path plate coupled with the nozzle plate and including a part of apressure chamber communicating with the nozzle opening; and a vibrationplate constituting a part of the pressure chamber, wherein the inactiveregion of the piezoelectric unit according to claim 1 is fixed to a flatfixing substrate at a predetermined position, and the first end portionis disposed in contact with the vibration plate.
 6. A liquid ejectinghead, comprising: a nozzle plate perforated with nozzle openings throughwhich a liquid is ejected; a flow path plate coupled with the nozzleplate and including a part of a pressure chamber communicating with thenozzle opening; and a vibration plate constituting a part of thepressure chamber, wherein the inactive region of the piezoelectric unitaccording to claim 2 is fixed to a flat fixing substrate at apredetermined position, and the first end portion is disposed in contactwith the vibration plate.
 7. A liquid ejecting head, comprising: anozzle plate perforated with nozzle openings through which a liquid isejected; a flow path plate coupled with the nozzle plate and including apart of a pressure chamber communicating with the nozzle opening; and avibration plate constituting a part of the pressure chamber, wherein theinactive region of the piezoelectric unit according to claim 3 is fixedto a flat fixing substrate at a predetermined position, and the firstend portion is disposed in contact with the vibration plate.
 8. A liquidejecting head, comprising: a nozzle plate perforated with nozzleopenings through which a liquid is ejected; a flow path plate coupledwith the nozzle plate and including a part of a pressure chambercommunicating with the nozzle opening; and a vibration plateconstituting a part of the pressure chamber, wherein the inactive regionof the piezoelectric unit according to claim 4 is fixed to a flat fixingsubstrate at a predetermined position, and the first end portion isdisposed in contact with the vibration plate.
 9. A liquid ejectingapparatus, comprising the liquid ejecting head according to claim
 5. 10.A liquid ejecting apparatus, comprising the liquid ejecting headaccording to claim
 6. 11. A liquid ejecting apparatus, comprising theliquid ejecting head according to claim
 7. 12. A liquid ejectingapparatus, comprising the liquid ejecting head according to claim 8.